FIG. 9 schematically shows the cross-sectional structure of a conventional annealing system, and specifically, a furnace type annealing system (a hot wall type annealing system).
The annealing system 100 of FIG. 9 includes a vertical furnace 101 of SiC and a coil 102 coiled around the side face of the furnace 101. The inside of the furnace 101 is heated with the coil 102 and kept at a predetermined temperature. Specifically, a temperature gradient is formed in a thermal region Rth within the furnace 101, and for example, the temperature of an upper portion of the thermal region Rth is set to a relatively high temperature of, for example, 1050° C., and the temperature of a lower portion of the thermal region Rth is set to a relatively low temperature of, for example, 850° C.
The annealing system 100 further includes a table 103 for placing a substrate 10 to be annealed and a support 104 for supporting and vertically moving the table 103. The substrate 10 can be held in an arbitrary position within the thermal region Rth by vertically moving the table 103, so that the substrate 10 can be annealed at a desired temperature. FIG. 9 shows a state where the table 103 is in an initial position H0 employed before starting the annealing of the substrate 10. Also, the table 103 holds the substrate 10 so that the reverse face of the substrate 10 can be partially exposed.
The annealing system 100 further includes a cover 105 for housing the furnace 101, the coil 102 and the table 103, and a substrate inlet/outlet 106 provided on the cover 105. Specifically, the substrate 10 inserted into the cover 105 through the substrate inlet/outlet 106 is placed on the table 103 so as to be annealed at a desired temperature in the thermal region Rth. The end of the support 104 opposing the table 103 extends to the outside of the cover 105.
In order to find out the temperature of the substrate 10 being annealed, it is necessary to measure the emissivity (thermal emissivity) ε and the pyrometer intensity (radiance) I of the substrate 10 as described later. For this purpose, a photoirradiation section 107 for irradiating the reverse face of the substrate 10 placed on the table 103 with measuring light of a predetermined wavelength is provided on the bottom of the cover 105, and a measuring section 108 for measuring the emissivity ε and the pyrometer intensity I on the reverse face of the substrate 10 is provided outside the cover 105 below the support 104.
Now, the reason why the temperature T can be obtained on the basis of the emissivity ε and the pyrometer intensity I will be described. In general, the pyrometer intensity I of a blackbody is represented by the following formula I on the basis of Planck's formula of radiation:I(T, λ)=2πC1/λ5·(exp((C2/(λT))−1))  Formula 1
As shown in formula 1, the pyrometer intensity I of a blackbody is a function of the temperature T of the blackbody and the wavelength λ of the measuring light. In other words, the pyrometer intensity I is varied in accordance with the temperature T and the wavelength λ. In formula 1, C1 and C2 are constants.
Also, the pyrometer intensity I of a general object (nonblackbody) is represented by the following formula 2 using the emissivity ε of the object:I(T, λ)=ε(T, λ)·2πC1/λ5·(exp((C2/(λT))−1))  Formula 2
As shown in formula 2, the emissivity ε is also a function of the temperature T of the object and the wavelength λ of the measuring light. Accordingly, in the case where the wavelength λ has a specific value, the temperature T is a function of the emissivity ε and the pyrometer intensity I, which is represented by the following formula 3:T=f(ε(emissivity), I (pyrometer intensity))  Formula 3
As shown in formula 3, the actual temperature T of an object being annealed can be obtained by measuring the emissivity ε and the pyrometer intensity I. In formula 3, f indicates a function (temperature measurement function) having variables ε and I. Also, in the case where the measuring light irradiating an object is entirely reflected by the object, the emissivity ε of the object is 0, and in the case where the measuring light irradiating an object is entirely absorbed by the object (namely, in the case where the object is a blackbody), the emissivity ε of the object is 1. In other words, when the reflectance of the measuring light is r, ε=1−r. Accordingly, instead of directly measuring the emissivity ε, the reflectance r can be measured so as to indirectly measure the emissivity ε by using the measured reflectance r.
As described above, in the annealing system 100 of FIG. 9, the whole thermal region Rth of the furnace 101 does not have a uniform temperature but the temperature gradient is formed in the thermal region Rth. Specifically, the temperature is higher toward the upper portion of the furnace 101. Accordingly, in order to anneal the substrate 10 at a desired temperature, the position within the furnace 101 in which the substrate 10 is held by using the table 103 and the support 104 is significant. At this point, for feedback control of the annealing temperature for the substrate 10, it is necessary to measure the emissivity ε and the pyrometer intensity I, so as to obtain the temperature of the substrate 10 being annealed on the basis of the measurement result. In the conventional technique, however, it is difficult to accurately obtain the temperature of the substrate 10 being annealed.